This invention relates to improved halogenated bisimide flame retardant products, to their manufacture, and to compositions containing a flammable material and such flame retardant products.
As is taught in U.S. Pat. No. 4,374,220, there are a multitude of halogenated bisimides which are effective as flame retardants in formulation with macromolecular flammable materials, e.g. polymers. These formulations are useful in making articles such as wire insulation and electronic housings. Of the halogenated bisimides, the N,N'-alkylene-bis-(tetrabromophthalimide)s are especially commercially significant.
A presently used commercial route for producing a product which principally contains N,N'-alkylene-bis-(tetrabromophthalimide) comprises reacting tetrabromophthalic anhydride with a diaminoalkane in the presence of water and an alkanoic acid to yield a reaction mass containing the intermediate, N,N'-alkylene diammonium-bis-(tetrabromophthalate). The reaction mass is then heated to about 210.degree. C. for a period of about 8 hours to convert the intermediate to N,N'-alkylene-bis-(tetrabromophthalimide) which is the principal constituent of the product recovered from the reaction mass. This product is particularly useful as it has good thermal stability and resistance to UV degradation. However, the product has a yellow color which argues against its presence in compositions used for forming white articles. Also, the intensity of the yellow color can vary between product batches, which color variance makes it difficult for the article manufacturer to maintain consistency in the color of the articles produced. The yellow color is believed to be due to impurities formed during the conversion of the N,N',-alkylene diammonium-bis-(tetrabromouphthalate intermediate to the corresponding bisimide product.
It is, therefore, an object of this invention to provide a process for producing a white flame retardant product which principally contains N,N'-alkylene-bis-(tetrabromophthalimide) or N,N'-bis-(tetrabromophthalimide), which product has high thermal stability and resistance to UV degradation.
It is also an object of this invention to provide a formulation which contains a macromolecular flammable constituent and the product of this invention wherein the color of articles formed from the formulation are not significantly affected by a yellow color contribution from the product during article formation